A technique of manufacturing a conventional loudspeaker diaphragm will be described with reference to a sectional view of the loudspeaker in FIG. 6 and a schematic view of a paper forming machine in FIG. 7.
The loudspeaker shown in FIG. 6 comprises magnetic circuit 1 comprising lower plate 1a with a center pole, magnet 1b, upper plate 1c, and magnetic gap 1d; frame 2; conical diaphragm 3 with its outer periphery bonded to the frame 2 via edge 3a and its inner periphery bonded to voice coil 4; and damper 5.
As the diaphragm 3, a plastic or metal-sheet diaphragm is available, but a paper sheet is generally employed as a loudspeaker diaphragm. Paper is excellent in physical properties such as large internal loss and rigidity that are basically required for a loudspeaker diaphragm, and also, it has various features such as being inexpensive and being amenable to manufacture by blending various kinds of pulp to obtain characteristics appropriate for each application.
A manufacturing method for the diaphragm made of a paper sheet will be described with reference to FIG. 7.
In FIG. 7, the diaphragm manufacturing apparatus comprises paper tank 11 for feeding dispersed pulp after beating, paper mold 12 made of wire mesh or the like, measuring tank 13 for material pulp dispersed in water, feed pipe 14, feed valve 15, water inlet pipe 16 for diluting the dispersed pulp, inlet valve 17, drain pipe 18, and drain valve 19.
The paper forming process using the above apparatus will be described in the following.
First, water is supplied from the dilution water inlet pipe 16, and after the water level becomes higher than the paper mold 12, the pulp dispersion measured by the measuring tank 13 is supplied into the paper tank 11. After that, the pulp dispersion in the paper tank 11 is stirred by air or other stirring means 10.
After predetermined amounts of pulp dispersion and dilution water are supplied into the paper tank 11, and uniformly stirred, the pulp material in the paper tank 11 begins to slowly deposit on the paper mold 12. To finish this process in a short time, it is a common method to rapidly drain the water from the drain pipe 18. This method is called a draw-down method. At the time, a swirl is generated near the drain port of the paper tank 11, and the pulp rotated due to the swirl in the paper tank 11 is deposited on the paper mold 12. The pulp deposited on the paper mold 12 is taken out and dried, and then the central and peripheral portions thereof are cut off to obtain the diaphragm 3 shown in FIG. 6.
Besides the above method, there is a method like a traditional manual paper forming method as is employed in manufacturing Japanese paper. In this method, a net is put into the water tank and is slightly moved in all directions to regulate a thickness and orientation in a skillful manner, which is then taken out of the water. This is a so-called draw-up method.
The formed paper is dried to be a loudspeaker diaphragm as required. In this case, it is preferable to dry the loudspeaker diaphragm naturally. However, in the case of an industrial production, it is a common method to employ hot air, hot press, and flames individually or in combination in order to efficiently dry the diaphragm in a short time.
Although the diaphragm 3 using pulp is inexpensive and can be easily provided with desired sound characteristics by blending various kinds of pulp, it is difficult to control the variation of pulp deposition on the paper mold 12 in the paper forming process. Therefore, it is liable to cause variations in sound characteristics of a loudspeaker. On the other hand, as sound sources are recently becoming digital and higher in performance, it is increasingly required to develop a method of manufacturing loudspeaker diaphragms with highly accurate reproducibility.
The present invention is intended to address the above problems and to provide a manufacturing method and manufacturing apparatus of a diaphragm, a diaphragm manufactured by the method, and a loudspeaker using the diaphragm.